Whistle Responder
Beeps when hears your whistle A gadget suitable for key-holders, games etc.
Circuit diagram:
Parts:
Device purpose:
Some 15 years ago it was common to see small key-holders emitting an intermittent beep for a couple of seconds after its owner whistled. These devices contained a special purpose IC and therefore were not suited to home construction. The present circuit is designed around a general purpose hex-inverter CMos IC and, using miniature components and button clock-type batteries can be enclosed in a matchbox. It is primarily a gadget, but everyone will be able to find suitable applications.
Circuit operation:
This device beeps intermittently
for approx. two seconds when a person in a range of about 10 meters emits a whistle.
The first two inverters contained
in IC1 are used as audio amplifiers.
IC1A amplifies consistently
the signal picked-up by the small
electret-microphone and
IC1B acts as a band-pass filter, its frequency
being centered at about 1.8KHz. The filter is
required in order to select a specific frequency, the whistle's one,
stopping other frequencies that would cause undesired
beeper's operation. IC1C is wired as a Schmitt
trigger, squaring the incoming audio signal. IC1D is a
2 second (approx.) monostable driving the astable formed
by IC1E & IC1F. This oscillator generates a 3 to 5Hz square wave
feeding Q1 and BZ1, thus providing intermittent beeper's operation.
Notes:
|
